In a long-range shooting, many factors that might not affect in a short-range shooting have a large impact on the ability to hit a target with dead-on accuracy. “Cant”, which is defined as a tilting of a rifle/bow (projectile launcher or the like) to one side relative to the vertical axis of the earth, is one of those factors. Long-range shooters have long used rifle/bow scopes with levels to eliminate canting. The level is generally mounted either on the rifle/bow or on the rifle/bow scope, specifically on top of the rifle/bow scope tube, side of the rifle/bow scope tube, or on top of the rifle/bow. When aiming at the target with the rifle/bow scope, the long-range shooters need to make sure that the level on the rifle/bow or the rifle/bow scope is leveled by looking at the level and that the target is on the aiming point through an eyepiece of the rifle/bow scope at the same time. However, one-eyed shooters can focus on one or the other and even two-eyed shooters may have difficult time in paying the same degree of attentions to both the level and the eyepiece of the rifle/bow scope. As a result, this creates a subtle canting which results in a significant deviation from the planned impact point. In general, 6 degrees of a canting in 1,000-yard (i.e., 914 m) long-range shooting creates up to 3 feet (i.e., 91.4 cm) deviation from the target, which can result in missing the target.
Therefore, it would be desirable to provide an apparatus that cures the deficiencies of prior approaches.